We propose a randomized controlled trial in 68 primary car practices in two medium size cities to determine the extent to which an innovative intervention through Independent Practice Associations (IPA's), based on small peer groups and in-office support to promote adoption of an effective cancer prevention office system, will increase the performance of preventive activities for four cancers (screening for breast, cervical, and colorectal cancers, and smoking cessation counseling for lung cancer), compared with practices exposed only to a standard quality assurance program used by IPA plans. Practices will be randomized into one of two condiitons. The control group practices will receive the "standard" (STD) quality assurance program used by the IPA's. The "peer group and office "(PG&O) intervention will receive the standard approach, plus an offer through their IPAs for a special program,beginning with identifying an "opinion leader" physician and office staff member within act practice who will agree to attend small peer group sessions six times/year for two years to find ways to optimize cancer prevention in their practices and to write a manual for other practices. The purpose of these groups is to allow participants in an early "stage of adoption" to step back from their practices and appropriately prioritize cancer prevention activities, and to be exposed to similar physicians and office staff in a later stage of adoption. When the physician-office staff pairs from each practice are ready, the project will work with them to institute a process, such as continuous quality improvement, to allow their practice to design and implement a cancer prevention office system, tailored to the special needs of the practice. They will receive support for skills training, system options, and computer assessment the proportion of eligible patients with documented performance of the cancer prevention activities in PG&O as compared with STD practices, as determined by medical record reviews. We will also examine whether the intervention has a differential effect for different activities or on different patient groups, such as those having IPA insurance coverage or those w ho are members of a disadvantaged group. We will also follow over time the association of change in the IPA approach to quality assurance with change in documented performance of the cancer prevention activities.